Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934728Ab2JXNSy (ORCPT ); Wed, 24 Oct 2012 09:18:54 -0400 Received: from mail.lemote.com ([222.92.8.141]:45317 "EHLO lemote.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934678Ab2JXNSx (ORCPT ); Wed, 24 Oct 2012 09:18:53 -0400 Message-ID: <4259.58.209.249.125.1351082073.squirrel@mail.lemote.com> Date: Wed, 24 Oct 2012 20:34:33 +0800 (CST) Subject: Re: [RFC][PATCH] sched: Fix a deadlock of cpu-hotplug From: =?gb2312?Q?=B3=C2=BB=AA=B2=C5?= To: "Peter Zijlstra" Cc: "Ingo Molnar" , linux-kernel@vger.kernel.org, "Fuxin Zhang" , "Thomas Gleixner" , "Srivatsa S. Bhat" , "Tejun Heo" User-Agent: SquirrelMail/1.4.11 MIME-Version: 1.0 Content-Type: text/plain;charset=gb2312 Content-Transfer-Encoding: 8bit X-Priority: 3 (Normal) Importance: Normal Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5655 Lines: 130 > On Wed, 2012-10-24 at 17:25 +0800, Huacai Chen wrote: >> We found poweroff sometimes fails on our computers, so we have the >> lock debug options configured. Then, when we do poweroff or take a >> cpu down via cpu-hotplug, kernel complain as below. To resove this, >> we modify sched_ttwu_pending(), disable the local irq when acquire >> rq->lock. >> >> [ 83.066406] ================================= >> [ 83.066406] [ INFO: inconsistent lock state ] >> [ 83.066406] 3.5.0-3.lemote #428 Not tainted >> [ 83.066406] --------------------------------- >> [ 83.066406] inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage. >> [ 83.066406] migration/1/7 [HC0[0]:SC0[0]:HE1:SE1] takes: >> [ 83.066406] (&rq->lock){?.-.-.}, at: [] >> sched_ttwu_pending+0x64/0x98 >> [ 83.066406] {IN-HARDIRQ-W} state was registered at: >> [ 83.066406] [] __lock_acquire+0x80c/0x1cc0 >> [ 83.066406] [] lock_acquire+0x60/0x9c >> [ 83.066406] [] _raw_spin_lock+0x3c/0x50 >> [ 83.066406] [] scheduler_tick+0x48/0x178 >> [ 83.066406] [] update_process_times+0x54/0x70 >> [ 83.066406] [] tick_handle_periodic+0x2c/0x9c >> [ 83.066406] [] c0_compare_interrupt+0x8c/0x94 >> [ 83.066406] [] handle_irq_event_percpu+0x7c/0x248 >> [ 83.066406] [] handle_percpu_irq+0x8c/0xc0 >> [ 83.066406] [] generic_handle_irq+0x48/0x58 >> [ 83.066406] [] do_IRQ+0x18/0x24 >> [ 83.066406] [] mach_irq_dispatch+0xe4/0x124 >> [ 83.066406] [] ret_from_irq+0x0/0x4 >> [ 83.066406] [] console_unlock+0x3e8/0x4c0 >> [ 83.066406] [] con_init+0x370/0x398 >> [ 83.066406] [] console_init+0x34/0x50 >> [ 83.066406] [] start_kernel+0x2f8/0x4e0 >> [ 83.066406] irq event stamp: 971 >> [ 83.066406] hardirqs last enabled at (971): [] >> local_flush_tlb_all+0x134/0x17c >> [ 83.066406] hardirqs last disabled at (970): [] >> local_flush_tlb_all+0x48/0x17c >> [ 83.066406] softirqs last enabled at (0): [] >> copy_process+0x510/0x117c >> [ 83.066406] softirqs last disabled at (0): [< (null)>] >> (null) >> [ 83.066406] >> [ 83.066406] other info that might help us debug this: >> [ 83.066406] Possible unsafe locking scenario: >> [ 83.066406] >> [ 83.066406] CPU0 >> [ 83.066406] ---- >> [ 83.066406] lock(&rq->lock); >> [ 83.066406] >> [ 83.066406] lock(&rq->lock); >> [ 83.066406] >> [ 83.066406] *** DEADLOCK *** >> [ 83.066406] >> [ 83.066406] no locks held by migration/1/7. >> [ 83.066406] >> [ 83.066406] stack backtrace: >> [ 83.066406] Call Trace: >> [ 83.066406] [] dump_stack+0x8/0x34 >> [ 83.066406] [] print_usage_bug+0x2ec/0x314 >> [ 83.066406] [] mark_lock+0x3fc/0x774 >> [ 83.066406] [] __lock_acquire+0x8a8/0x1cc0 >> [ 83.066406] [] lock_acquire+0x60/0x9c >> [ 83.066406] [] _raw_spin_lock+0x3c/0x50 >> [ 83.066406] [] sched_ttwu_pending+0x64/0x98 >> [ 83.066406] [] migration_call+0x10c/0x2e0 >> [ 83.066406] [] notifier_call_chain+0x44/0x94 >> [ 83.066406] [] __cpu_notify+0x30/0x5c >> [ 83.066406] [] take_cpu_down+0x5c/0x70 >> [ 83.066406] [] stop_machine_cpu_stop+0x104/0x1e8 >> [ 83.066406] [] cpu_stopper_thread+0x110/0x1ac >> [ 83.066406] [] kthread+0x88/0x90 >> [ 83.066406] [] kernel_thread_helper+0x10/0x18 > > Weird, that's from a CPU_DYING call, I thought those were with IRQs > disabled. > > Look at how __stop_machine() calls the function with IRQs disabled for ! > stop_machine_initialized or !SMP. Also stop_machine_cpu_stop() seems to > disabled interrupts, so how do we end up calling take_cpu_down() with > IRQs enabled? > > That simply doesn't make any sense. I see, this is an arch-specific bug, sorry for my carelessness and thank you for your tips. > >> Signed-off-by: Huacai Chen >> --- >> kernel/sched/core.c | 5 +++-- >> 1 files changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 36e2666..703754a 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -1468,9 +1468,10 @@ static void sched_ttwu_pending(void) >> { >> struct rq *rq = this_rq(); >> struct llist_node *llist = llist_del_all(&rq->wake_list); >> + unsigned long flags; >> struct task_struct *p; >> >> - raw_spin_lock(&rq->lock); >> + raw_spin_lock_irqsave(&rq->lock, flags); >> >> while (llist) { >> p = llist_entry(llist, struct task_struct, wake_entry); >> @@ -1478,7 +1479,7 @@ static void sched_ttwu_pending(void) >> ttwu_do_activate(rq, p, 0); >> } >> >> - raw_spin_unlock(&rq->lock); >> + raw_spin_unlock_irqrestore(&rq->lock, flags); >> } >> >> void scheduler_ipi(void) > > > That's wrong though, you add the cost to the common case instead of the > hardly ever ran hotplug case. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/